Another 60% came from changes to wind or ocean current patterns over the tropical Atlantic Ocean. The result was more warmed water reaching the southern East Coast and the Gulf.
Higher sea levels and active hurricane seasons, 2017-2022: The lines with color-filled symbols are storm tracks, plotted at 6-hour intervals. The color of symbols indicates storm density, from tropical storm, green, to Category 5, dark red. Thick black lines on the paths indicate high-impact hurricanes: Harvey in 2017, Florence and Michael in 2018, Laura in 2020, Ida in 2021, and Ian in 2022. Color shadings in water areas shows sea level anomalies in each year relative to long-term annual mean during 1993-2012, with darker colors indicating higher water levels. Note that hurricanes tend to intensify rapidly in passing over highher sea level and ocean heat content regions in the Gulf. Warmer water generally is higher. (Janjun Yin, Journal of Climate)
“What makes it more complicated in Louisiana and Texas is the subsidence that comes on top of that, and that leads to rates of 14 to 15 millimeters a year,” Dangendorf said.
Warmer waters
Part of that natural variability, he said, is a 25- to 40-year cycle linked to lower and higher water temperatures in the Atlantic, called the Atlantic Multi-Decadal Oscillation.
Many climate scientists who study hurricanes believe that a warmer water version of that cycle began in 1995 and has stirred more frequent hurricanes.
The bright side of that finding is that sea-rise could slow back to the pre-2010 rate of 1.5 mm a year in about a decade.
Yet even that lower global rate, a mainstay since 1900, marked a significant increase in sea-level rise from the previous 3,000 years, the study found.
Sea level rise along the U.S. East and Gulf Coasts from the tide gauge data (1920-2022). (a) New England; (b) Mid-Atlantic; (c) Southeast; and (d) Eastern Gulf. The red curves are the mean of the tide gauge data in the same region relative to the period of 1920-1940. The number of tide gauge stations used for calculating the regional mean is shown by the blue bars at the bottom of each panel. The blue dashed line is the linear regression for sea level during 1920-2009. It is extrapolated to 2022 to show the sea level departure during 2010-2022. For (c) and (d), the linear regression for the 2010-2022 period is also plotted (brown dashed lines). The black solid line is the global mean sea level rise during 1993-2021 from altimetry data. The vertical green line marks year 2010. (Jianjun Yin, Journal of Climate)
In his study, Yin discounted nearshore winds and changes in barometric pressure along coastlines as leading causes of the increase in sea level rise.
The loop
His research found another trend: more warm water feeding into the Gulf Stream and the Gulf of Mexico from a significant slowdown of a large, north-south oceanic pattern.
Yin argues that a downshift in the Atlantic Meridional Overturning Circulation, beginning in 2009 and 2010, injected even more warmth into the deep Loop Current, a segment of the Gulf Stream that breaks off every year or so and floats around the Gulf.
That bloated the size of water molecules, adding to sea level rise.
Yin also linked the acceleration to the heights of hurricane-induced storm surge in recent years.
He measured the surge and sea levels at local gauges from Texas to North Carolina over a half-dozen massive hurricanes: Harvey in 2017; Florence and Michael in 2018; Laura in 2020; Ida in 2021; Ian in 2022.
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